What to know about the latest fighting between Afghanistan and Pakistan

Pakistan's defense minister says there is a state of “open war” with Afghanistan

ISLAMABAD -- Pakistan is in an “open war” with Afghanistan, Defense Minister Khawaja Mohammad Asif said Friday, with fighting escalating into the most serious armed confrontation between the two uneasy neighbors since a Qatari-mediated ceasefire in October.

The two countries share a long, complicated history harking back to Pakistan's creation in 1947. Bound by traditional social, ethnic and economic ties, relations have nonetheless been volatile and have often descended into armed conflict.

Over the last few months, the two have occasionally skirmished along their winding, porous frontier as tension has escalated. The latest confrontation is by far the most serious.

Here are some key things to know about the two countries' relations and why they are fighting.

Afghanistan launched an extensive cross-border attack into Pakistan along six provinces on Thursday night, in what it said was retaliation for Pakistani airstrikes on Afghanistan on Sunday. Pakistan had said those airstrikes had targeted and killed dozens of militants in Afghanistan, but Kabul said only civilians, including women and children, had been killed.